In many aircraft braking systems, a pilot typically adjusts the braking effort with a pair of brake pedals, the degree of brake pedal depression demanding a related brake pressure. The resulting brake torque and deceleration of the aircraft vary, however, as a function of the physical characteristics of the associated brake assemblies.
In many aircraft, it is desirable that the braking system be deceleration based such that pedal depression correlates with a specific demand for deceleration. By way of example, half pedal depression could correlate with a deceleration rate of 10 ft/sec.sup.2, while quarter pedal depression would correlate with a deceleration rate of 5 ft/sec.sup.2. In such systems, the deceleration rate of the aircraft is substantially independent of the relationship between brake pressure and brake torque.
Automatic braking systems are known in the aircraft industry. While the same typically constitute a deceleration based system, they typically operate independent of the pilot. Once the pilot selects a desired deceleration rate, braking control is removed from the pilot and is totally controlled through automatic system operation. Such is most undesirable in many braking situations, particularly where it is necessary for the pilot to retain steering capabilities. Since ground steering of an aircraft is typically controlled by braking operations, known automatic braking systems are ineffective to allow the pilot to maintain the requisite control.
A unique problem arises in braking systems where it is desired to maintain left and right brake control through left and right pedals, while attaining deceleration-based brake control. Specifically, a single deceleration (acceleration) signal is associated with the aircraft as a whole, while separate left and right brake control signals are produced from left and right brake pedals. Unless special measures are taken, the resultant control would be left-right unstable. In other words, the larger command signal, from either the left or right brake pedal, would shut off the smaller command signal. Only when both command signals are equal would the braking be symmetrical. This results in the system having two sources of control input signals (brake pedals) and a single feedback signal correlated to vehicle deceleration.
It is most desirable to provide a pilot-controlled deceleration-based braking system for aircraft, allowing the pilot to brake the aircraft at pedal-selected deceleration rates, while maintaining left-right braking and steering control.